Removing the key query parameter from the authentication call.

Meetup has made a change to their OAuth implementation. It returns
an error when using two forms of authentication.

You can refer to this url for a little history on the problem.
https://groups.google.com/forum/?fromgroups=#!topic/meetup-api/Ox1NG2mplkU
Merge pull request #4 from russ/master

Meetup OAuth2 change